1. Field of Invention
The present invention relates to a liquid crystal display and a method for driving the same, wherein one or more horizontal lines carrying no data among horizontal lines of a progressive-processed frame can be compensated with data.
2. Discussion of the Related Art
A liquid crystal display (LCD) displays an image by controlling optical transmittance of liquid crystal (LC) cells according to video signals. An active matrix LCD, which includes switching elements formed respectively at LC cells, is advantageous in implementing moving images since it can actively control the switching elements. As shown in FIG. 1, a thin film transistor (TFT) is typically used as each switching element of the active matrix LCD.
The active matrix LCD is driven in the following manner. As shown in FIG. 1, digital input data is converted into an analog data voltage based on a gamma reference voltage and the analog data voltage is provided to a data line DL while a scan pulse is then provided to a gate line GL to charge an LC cell Clc.
A gate electrode of the TFT is connected to the gate line GL, a source electrode of the TFT is connected to the data line DL, and a drain electrode of the TFT is connected to one end of a storage capacitor Cst and one end of the LC cell Clc.
A common voltage Vcom is provided to a common electrode of the LC cell Clc.
The storage capacitor Cst is charged to the data voltage applied from the data line DL when the TFT is turned on, and maintains the voltage of the LC cell Clc constant.
When a scan pulse is applied to the gate line GL, the TFT is turned on so that a channel is formed between the source and drain electrodes, thereby allowing the voltage on the data line DL to be applied to the pixel electrode of the LC cell Clc. Thus, an electric field produced between the pixel and common electrodes changes the arrangement of LC molecules of the LC cell Clc, thereby modulating light incident on the LC cell Clc.
The LCD, which includes pixels, each having the structure described above, is generally used as a display component of a video display device such as a television receiver or a computer monitor.
The television receiver having the LCD uses a 2D deinterlacer or a 3D deinterlacer provided in it to convert an interlaced signal input from a base station into a progressive signal. However, the television receiver generally uses the 2D deinterlacer since the 2D deinterlacer is low-priced while the 3D deinterlacer is expensive.
How the interlaced signal and the progressive signal are produced will now be described with reference to FIG. 2.
As shown in FIG. 2, a frame A1 captured by a camera, which includes an original signal, is converted into a top field A2 and a bottom field A3, each including an interlaced signal, through a sampling process performed at a base station or the like. The top field A2 and the bottom field A3 are then transmitted to a television receiver.
The top field A2 includes odd horizontal lines carrying no data and even horizontal lines carrying data. The data carried in the even horizontal lines of the top field A2 is the same as that carried in even horizontal lines of the frame A1 including the original signal.
The bottom field A3 includes odd horizontal lines carrying data and even horizontal lines carrying no data. The data carried in the odd horizontal lines of the bottom field A3 is the same as that carried in odd horizontal lines of the frame A1 including the original signal.
When the television receiver inputs the top field A2 and the bottom field A3, a 2D deinterlacer in the television receiver converts the top field A2 including an interlaced signal into an even frame A4 including a progressive signal while converting the bottom field A3 including an interlaced signal into an odd frame A5 including a progressive signal.
Specifically, the 2D deinterlacer fills data in the odd horizontal lines carrying no data among the horizontal lines of the top field A2, thereby converting the top field A2 including an interlaced signal into the even frame A4 including a progressive signal. That is, data of the even horizontal lines of the even frame A4 is kept identical to that of the even horizontal lines of the top field A2, while the odd horizontal lines of the even frame A4 are filled with data by the 2D deinterlacer. The data filled in the odd horizontal lines of the even frame A4 is produced using the data carried in the even horizontal lines of the top field A2. Specifically, each odd horizontal line of the even frame A4 is filled with an average value of the data of a pair of even horizontal lines vertically adjacent to the odd horizontal line.
On the other hand, the 2D deinterlacer fills data in the even horizontal lines carrying no data among the horizontal lines of the bottom field A3, thereby converting the bottom field A3 including an interlaced signal into the odd frame A5 including a progressive signal. That is, data of the odd horizontal lines of the odd frame A5 is kept identical to that of the odd horizontal lines of the bottom field A3, while the even horizontal lines of the odd frame A5 are filled with data by the 2D deinterlacer. The data filled in the even horizontal lines of the odd frame A5 is produced using the data carried in the odd horizontal lines of the bottom field A3. Specifically, each even horizontal line of the odd frame A5 is filled with an average value of the data of a pair of odd horizontal lines vertically adjacent to the even horizontal line.
When the television receiver converts a input interlaced signal into a progressive signal using the 2D deinterlacer included in it and displays a corresponding image on the LCD, data is alternately absent and present in a series of consecutive frames (N−1th Frame, Nth Frame, N+1th Frame, and N+2th Frame), such that data is absent in the frames (N−1th Frame and N+1th Frame) as shown in FIG. 3. Since the LCD performs polarity inversion to reverse the polarity of data on a frame by frame basis, the N−1th and N+1th frames have data of the same polarity while Nth and N+2th frames have data of the same polarity which is opposite to that of the N−1th and N+1th frames.
Accordingly, if the N−1th and N+1th frames have no data as shown in FIG. 3, the N−1th and N+1th frames having no data are not displayed on the LC panel, while the Nth and N+2th frames having data are displayed on the LC panel. That is, data of the same polarity is continuously provided to each pixel of the LCD since the data in the Nth and N+2th frames with the same polarity is provided to the LC panel.
Flickering occurs in images displayed on the LCD if data is absent in one of a series of neighboring frames as described above. In addition, if data of the same polarity is continuously provided to each pixel of the LCD, after-image occurs and liquid crystal is degraded due to drive characteristics of LC molecules provided in each pixel.